This invention relates generally to an electrophotographic printing machine, and more particularly, concerns an apparatus for transferring a developed image from a photoconductive surface to a sheet.
A typical electrophotographic printing machine employs a photoconductive member that is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image. Exposure of the charged photoconductive surface selectively dissipates the charge thereon in the irradiated areas to record an electrostatic latent image on the photoconductive surface corresponding to the informational areas being reproduced by the printing machine. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed by bringing a developer material into contact therewith. Generally, the electrostatic latent image is developed with dry developer material having carrier granules with toner particles adhering thereto. However, a liquid developer material may be used as well. The toner particles are attracted to the latent image forming a visible image on the photoconductive surface. After the electrostatic latent image is developed with the toner, the toner image is transferred to a sheet. The toner image is then heated to permanently fuse it to the sheet.
High speed commercial printing machines of the foregoing type handle a wide range of differing weight sheets. The beam strength of the sheet is a function of the weight of the sheet. Heavy weight sheets have greater beam strength than lighter weight sheets. It is not unusual for the sheet to be cockled before it is transported to the processing station where the developed image is transferred to the sheet. The second side of duplex sheets may also suffer from cockle due to the image on the first side and the effect of the fuser on the sheet. This is the single greatest cause for cockle. The stack of sheets placed in the sheet feeder may be initially cockled, or the sheets may become cockled as they are fed from the stack to the transfer station. At the transfer station, the sheet adheres to the photoconductive member. In the event the sheet is cockled, it is not held in intimate contact with the photoconductive surface, but rather spaces occur between the developed image on the photoconductive surface and the sheet. In the electrostatic transfer of the toner image to the sheet, it is necessary for the sheet to be in uniform, intimate contact with the toner powder image developed on the photoconductive surface. Failure to do so results in variable transfer efficiency and, in the extreme, areas of low or no transfer resulting in image deletions. Pretransfer sheet guides can be used to put an xe2x80x9cSxe2x80x9d bend in the sheet. This xe2x80x9cSxe2x80x9d bend will force the paper flat against the photoconductive surface as it enters the transfer region. The higher the degree of the xe2x80x9cSxe2x80x9d bend, the more normal a flattening force can be achieved. However, optimal sheet entry angles for lightweight sheets are not necessarily optimal for heavyweight sheets. Various types of baffle arrangements have been employed heretofore.
U.S. Pat. No. 5,311,267 (Bean), the disclosure of which is totally incorporated herein by reference, discloses a combination of a roller and baffle used to impart a curvilinear or S-shape to the sheet. The baffle may be moved to vary the shape of the sheet as the sheet moves into the transfer zone.
U.S. Pat. No. 5,678,122 (Gross), the disclosure of which is totally incorporated herein by reference, discloses a moveable baffle and a sheet basis weight sensing unit which detects the weight of the sheet. The signal from the sensing unit is sent to a controller which, in conjunction with an electromechanical device coupled thereto, moves the guide to provide the proper bend for the sheet.
There is provided an apparatus for transferring a developed image from an imaging member having a generally planar surface to a sheet, including: a sheet guide having an elongated axis extending in a transverse direction to the planar surface of the imaging member; said sheet guide including a roller assembly on a sheet exit portion of said sheet guide.
There is also provided an electrophotographic printing machine of the type in which a developed image from an imaging member having a generally planar surface to a sheet, including: a sheet guide having an elongated axis extending in a transverse direction to the planar surface of the imaging member; said sheet guide including a roller assembly on a sheet exit portion of said sheet guide.